200 FLAT WORMS. 



forms make their way to the liver where they develop. Arriving at 

 maturity, the males and females become united and proceed to the 

 terminal branches of the portal vein^ where the irritating eggs, given off 

 by the female, give rise to the symptoms. 



CESTODE OR TAPE- WORM INFECTIONS. 



The cestodes and trematodes constitute the two great divisions of 

 the flat-worms. Anatomically, a tape-worm may be considered as a 

 series of individual flukes united in one ribbon-like colony. The 

 cestode segments, or proglottides, differ, however, from the flukes in not 

 having an alimentary canal and in having a cellular instead of a 

 chitinous external covering. 



A tape-worm is divided, into the segment-producing controlling 

 head and the series of segments or proglottides together known as the 

 strobila. The head and neck together form the scolex. Tape-worm 

 heads are provided with suctorial or hook-like suckers, or both, to 

 enable them to hold on to the intestinal mucosa. The importance of 

 the head is generally recognized by the well-known fact that the per- 

 manent evacuation of one of these parasites is only arrived at when the 

 head as well as the segments is expelled. Otherwise, additional 

 segments will be produced. Even in tape-worms twenty-five to 

 thirty feet in length, the head is no larger than a small shot. It 

 carries the suckers or booklets which best enable us to differentiate 

 the different species. The segments adjacent to the head are im- 

 mature the sexually -mature ones being found from the middle of the 

 body onward. The sexually-mature segment possesses a varying 

 number of testicles: 3 in H. nana and as many as 2000 in T. saginata. 

 As with the flukes, they also have ovaries, yolk glands, uterus, genital 

 pore, etc. The location of the genital pore and the character of the 

 branching of the uterus are of the greatest importance in differentia- 

 tion. The sexually-mature proglottides may either expe their ova, 

 when these would be found in the faeces or, as is common, they break off 

 and pass out themselves in the faeces They then either expel the eggs 

 or may be eaten by some animal and in this way effect an entrance for 

 their ova. The "hexacanth" or 6-hooked embryo, also called the 

 onchosphere, is the essential part of the egg. The egg shell is dis- 



